Talk to me about boiler flow temp settings...
Discussion
Ive finally got my heating semi-sorted following installation of a new combi.
Now, what is the most cost effective way of running the boiler? If I set the flow temp to 60 the boiler is running virtually all day, whereas if I upped that to 70, then the boiler will be running less. So what's better for the pocket?
Background info- Old detached house (1860), heating target is 20 degrees
Now, what is the most cost effective way of running the boiler? If I set the flow temp to 60 the boiler is running virtually all day, whereas if I upped that to 70, then the boiler will be running less. So what's better for the pocket?
Background info- Old detached house (1860), heating target is 20 degrees
If it's a new combi, it may be adjusting the flow temp according to how much below target temp the house is.
This is load compensation or demand compensation and many boilers do it including mine.
Alternatively it may have 'weather comp' where the flow temp you ask for is not what you get, the boiler adjusts it according to the outdoor temperature.
Your flow temps sound very high. It would be helpful to know the radiator temperatures, if the TRVs are turning the rads down a lot then you might aw well lower the flow temp. But you may want to turn it back up again if the weather is cold and you want to heat the house quickly.
Quite possibly your boiler is modulating to quite low power and it's just a bit more stable at the lower flow temp because the flow rate is a bit higher and the boiler isn't overshooting its target flow temp.
A low flow temp and less cycling is more efficient, but the differences are smaller than some people would have you believe.
Keeping the flow temp lower can avoid/reduce wasteful overshoots of room temperature
This is load compensation or demand compensation and many boilers do it including mine.
Alternatively it may have 'weather comp' where the flow temp you ask for is not what you get, the boiler adjusts it according to the outdoor temperature.
Your flow temps sound very high. It would be helpful to know the radiator temperatures, if the TRVs are turning the rads down a lot then you might aw well lower the flow temp. But you may want to turn it back up again if the weather is cold and you want to heat the house quickly.
Quite possibly your boiler is modulating to quite low power and it's just a bit more stable at the lower flow temp because the flow rate is a bit higher and the boiler isn't overshooting its target flow temp.
A low flow temp and less cycling is more efficient, but the differences are smaller than some people would have you believe.
Keeping the flow temp lower can avoid/reduce wasteful overshoots of room temperature
Road2Ruin said:
You need to know the return temperature, to make it the most efficient. It should be less than 55c. From an 80c flow temp, in our house, the return drops to about 45c
How do you get a 35c drop on the flow/return?! Ours is set at 65c flow (it’s a system and I like hot water in the tank but I do drop to 60c) and the return is 55c. You must have some big boy rads. I need to work our heat loss but I suspect the rads are undersized.
PT1984 said:
Road2Ruin said:
You need to know the return temperature, to make it the most efficient. It should be less than 55c. From an 80c flow temp, in our house, the return drops to about 45c
How do you get a 35c drop on the flow/return?! Ours is set at 65c flow (it’s a system and I like hot water in the tank but I do drop to 60c) and the return is 55c. You must have some big boy rads. I need to work our heat loss but I suspect the rads are undersized.
PT1984 said:
How do you get a 35c drop on the flow/return?! Ours is set at 65c flow (it’s a system and I like hot water in the tank but I do drop to 60c) and the return is 55c.
You must have some big boy rads. I need to work our heat loss but I suspect the rads are undersized.
Is every radiator in your house averaging 60 degC, long term?You must have some big boy rads. I need to work our heat loss but I suspect the rads are undersized.
If you look at the outlet temp of every radiator, you might find that many of them are quite low, you just have one or two radiators (or even a bypass loop) returning hot water back to the boiler.
Or maybe your rads are all cool, throttled by the TRVs, all the flow is to the HW cylinder?
A combi boiler can run flow temps well below the hot water setting. It doesn't attempt to do HW and CH at the same time.
OutInTheShed said:
Is every radiator in your house averaging 60 degC, long term?
If you look at the outlet temp of every radiator, you might find that many of them are quite low, you just have one or two radiators (or even a bypass loop) returning hot water back to the boiler.
Or maybe your rads are all cool, throttled by the TRVs, all the flow is to the HW cylinder?
A combi boiler can run flow temps well below the hot water setting. It doesn't attempt to do HW and CH at the same time.
Now you mention it I had to have a bypass loop installed as the old boiler never had an overrun. That is valved though. I also have a towel rail on the rad loop. And that is the work of the devil with flow. I will shut both off and have a look. Rads are balanced and TBH I run the TRVs at full whack. I only have the house at 19.5c max. Thank you. If you look at the outlet temp of every radiator, you might find that many of them are quite low, you just have one or two radiators (or even a bypass loop) returning hot water back to the boiler.
Or maybe your rads are all cool, throttled by the TRVs, all the flow is to the HW cylinder?
A combi boiler can run flow temps well below the hot water setting. It doesn't attempt to do HW and CH at the same time.
Edited by PT1984 on Sunday 24th November 07:31
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